Speeding up early pedogenetic processes in constructed Technosols with organic matter enrichment

Constructed soils (Technosols) produced from waste materials offer a sustainable alternative to landfill disposal while supporting vegetation and ecosystem services, without relying on topsoil extracted from natural areas. Research in pedological engineering aims to design functional soils through the recycling of low-value materials, thereby contributing to a circular economy in urban environments. One poorly documented aspect of Technosol pedogenesis is the short-term impact of mixing parent materials with contrasting properties, which can trigger rapid soil formation processes within months—much faster than the years or centuries required for natural soils. This characteristic makes Technosols valuable experimental models for investigating pedogenic processes on time scales compatible with human observation. In this study, we examined how the properties and interactions of two parent materials—excavated deep soil horizons (EM) and green waste compost (GWC)—influence the rate of early pedogenetic processes. We hypothesised that increasing organic matter inputs through GWC addition would accelerate the physical, chemical, and biological processes leading to soil formation. To test this hypothesis, six EM/GWC mixtures (0–50% GWC, w/w) were incubated in mesocosms under controlled conditions for 21 weeks and subjected to repeated wet–dry cycles. Pedogenetic changes were assessed using chemical (C, N, available P, pH, CEC), hydrostructural (shrinkage curves), and biological indicators (catabolic profiles, qPCR, and molecular fingerprints). Results showed that increasing compost content significantly accelerated the evolution of soil properties. Organic matter losses were greater in GWC-rich Technosols due to enhanced mineralisation, leading to a slight but significant decrease in pH and increased nutrient release, particularly phosphorus. These changes were accompanied by an increase in cation exchange capacity, suggesting the development of organo-mineral associations and increased reactive surface area. Hydrostructural properties also evolved proportionally to initial GWC content, with higher compost inputs improving moisture retention in both macro- and micropores, increasing void ratios at the end of shrinkage, and enhancing available water capacity. These physical changes, promoted by higher organic matter content, strongly influenced microbial abundance, community composition, and metabolic activity. Overall, this study demonstrates that early pedogenetic processes in Technosols can be markedly accelerated by organic matter enrichment through its combined effects on chemical, physical, and biological soil properties. Our findings highlight the dual potential of Technosols as both functional soils for urban applications and powerful experimental systems for studying early soil formation.